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United States Patent |
6,012,520
|
Yu
,   et al.
|
January 11, 2000
|
Hydrocarbon recovery methods by creating high-permeability webs
Abstract
A gravity-drainage hydrocarbon recovery method is provided to produce oil
and gas from subterranean formations. A substantially horizontal
high-permeability web is created at the bottom portion of an oil
reservoir. The web is connected to a production well. The
high-permeability web is fabricated by conventional drilling,
high-pressure water jet drilling, and high-power microwave fracturing.
Primary oil recovery will benefit from this configuration in terms of
improved volumetric sweep efficiency, delayed gas break through, increased
oil production rate and overall oil recovery. This method is also used
with secondary oil recovery for which a gas is injected into the upper
portion of a reservoir. Oil is produced from the bottom portion of the
reservoir. If economically warranted, high-permeability web is also
implemented to the injection well. The method for this invention is also
used in conjunction with any horizontal and vertical well arrangement
methods, enhanced oil recovery methods, and methods used for oil field
conformance improvement.
Inventors:
|
Yu; Andrew (3528 W. Lake Dr., Martinez, GA 30907);
Tsou; Peter (5700 Braxton, Suite 190, Houston, TX 77036)
|
Appl. No.:
|
225527 |
Filed:
|
January 4, 1999 |
Current U.S. Class: |
166/245; 166/50; 166/248; 166/268; 166/272.7; 166/308.1 |
Intern'l Class: |
E21B 043/24; E21B 043/26; E21B 043/30 |
Field of Search: |
166/50,245,248,268,272.7,271,306,308
299/17
175/67
|
References Cited
U.S. Patent Documents
4022279 | May., 1977 | Driver | 166/271.
|
4754808 | Jul., 1988 | Harmon et al. | 166/245.
|
4889186 | Dec., 1989 | Hanson et al. | 166/245.
|
5082054 | Jan., 1992 | Kiamanesh | 166/248.
|
5273111 | Dec., 1993 | Brannan et al. | 166/245.
|
5299887 | Apr., 1994 | Ensley | 405/128.
|
5320170 | Jun., 1994 | Huang et al. | 166/245.
|
5363927 | Nov., 1994 | Frank | 299/17.
|
5413184 | May., 1995 | Landers | 175/62.
|
5875843 | Mar., 1999 | Hill | 166/308.
|
Primary Examiner: Suchfield; George
Attorney, Agent or Firm: Fulbright & Jaworski L.L.P.
Parent Case Text
This is a continuation, of application Ser. No. 08/731,334 filed Oct. 11,
1996, now abandoned. This application claims the benefits of application
Ser. No. 08/731,334 filed Oct. 11, 1996. This application incorporates by
reference the entire text of the 08/731,334 application.
Claims
We claim:
1. A method for enhancing recovery of hydrocarbons from a subterranean
formation comprising the steps of:
drilling a vertical production well into a hydrocarbon reservoir; and
creating a horizontal radial high-permeability web in the subterranean
formation proximal to a lower region of the hydrocarbon reservoir adjacent
to the vertical production well.
2. The method for enhancing recovery of hydrocarbons according to claim 1,
wherein the step of creating a high-permeability web comprises the steps
of:
lowering a high-powered microwave antenna into the vertical production
well; and
generating one or more microwave beams directed outwardly into the
surrounding formation from the antenna.
3. The method for enhancing recovery of hydrocarbons according to claim 2,
wherein the direction of said one or more microwave beams is substantially
horizontal.
4. The method for enhancing recovery of hydrocarbons according to claim 2,
wherein said one or more microwave beams are of a high intensity to
achieve maximum penetration.
5. The method for enhancing recovery of hydrocarbons according to claim 2,
wherein permeability of the formation is increased by an amount greater
than one Darcy.
6. The method for enhancing recovery of hydrocarbons according to claim 2,
wherein a plurality of microwave beams are simultaneously generated in
different directions to form the web comprising a corresponding plurality
of high permeability channels.
7. The method for enhancing recovery of hydrocarbons according to claim 1,
wherein the step of creating a high-permeability web comprises the steps
of:
lowering a flexible hose carrying a spray head on an end thereof into the
vertical well; and
generating one or more high-pressure water jet streams directed outwardly
into the surrounding formation from the spray head.
8. The method for enhancing recovery of hydrocarbons according to claim 7,
wherein a plurality of high-pressure waterjet streams are simultaneously
generated in different directions to form the web comprising a
corresponding plurality of high permeability channels.
9. The method for enhancing recovery of hydrocarbons according to claim 1,
further comprising the step of drilling one or more vertical injection
wells into an upper region of the hydrocarbon reservoir for injection of a
gas into the formation above the hydrocarbons to be recovered.
10. The method for enhancing recovery of hydrocarbons according to claim 9,
further comprising the step of creating a high-permeability web in an
upper region of the hydrocarbon reservoir proximal to a lower end of the
injection well.
11. The method for enhancing recovery of hydrocarbons according to claim 1,
further comprising the step of forming one or more horizontal wells
extending horizontally outward from a lower region of the vertical
production well.
12. The method for enhancing recovery of hydrocarbons according to claim
11, wherein the step of creating a high-permeability web comprises
creating a plurality of high-permeability webs extending outwardly from
said one or more horizontal wells.
13. The method for enhancing recovery of hydrocarbons according to claim
11, wherein said plurality of horizontal wells comprises four horizontal
wells, each one of said four horizontal wells being positioned 90.degree.
apart from each adjacent horizontal well.
14. The method for enhancing recovery of hydrocarbons according to claim
13, wherein the step of creating a high-permeability web comprises
creating a plurality of high-permeability webs, such that one or more high
permeability webs are formed extending outwardly into the subterranean
formation from each of the four horizontal wells.
15. The method for enhancing recovery of hydrocarbons according to claim
14, further comprising the step of drilling one or more vertical injection
wells into an upper region of the hydrocarbon reservoir for injection of a
gas into the formation above the hydrocarbons to be recovered.
16. A method for enhancing recovery of hydrocarbons from a subterranean
formation comprising the steps of:
drilling four vertical corner production wells in a square configuration
into a hydrocarbon reservoir;
drilling an injection well in the center of the square configuration;
forming one or more horizontal wells extending horizontally outward from a
lower region of each one of the four vertical corner production wells; and
creating one or more high-permeability webs extending outwardly from each
horizontal well.
17. The method for enhancing recovery of hydrocarbons according to claim
16, further comprising the step of creating a high-permeability web in an
upper region of the hydrocarbon reservoir proximal to a lower end of the
injection well.
18. A method for enhancing recovery of hydrocarbons from a subterranean
formation comprising the steps of:
drilling at least two upper horizontal wells into a hydrocarbon reservoir
in the formation;
drilling at least one lower horizontal well, each one of said at least one
lower horizontal well being spaced laterally and vertically below and
between two of said at least two upper horizontal wells, and wherein the
upper and lower horizontal wells are substantially parallel; and
creating a high-permeability web in the subterranean formation from one or
more points along a longitudinal axis of at least one of said upper and
lower horizontal wells.
19. The method for enhancing recovery of hydrocarbons according to claim
18, wherein high-permeability webs are created from one or more points
along the longitudinal axis of both said two or more upper horizontal
wells and said one or more lower horizontal well.
20. The method for enhancing recovery of hydrocarbons according to claim
18, wherein high-permeability webs are created from one or more points
along the longitudinal axis of each of said one or more lower horizontal
well.
21. The method for enhancing recovery of hydrocarbons according to claim
18, wherein high-permeability webs are created from one or more points
along the longitudinal axis of each of said two or more upper horizontal
wells.
Description
BACKGROUND OF THE INVENTION
The present invention relates to methods for recovering hydrocarbons from a
subterranean formation. The emphasis is on oil reservoirs. However, the
methods are also applicable to gas, gas condensate, shale oil and tar sand
formations. The fundamental technique used by the invention is to create a
horizontal, high-permeability web at the bottom portion of a reservoir.
This technique is made possible by recent developments in drilling and
microwave technologies.
One of the simple ways to produce oil is to drill a single vertical well
into an oil-bearing formation. Oil will be produced by the natural energy
within the reservoir, such as expansion of gas cap or solution gas drive.
After producing a fraction of the original oil in place (OOIP), it is
becoming less economically attractive to deplete the reservoir by this
primary recovery mechanism. A secondary production method is needed to
push the oil through the formation. The basic scheme for secondary
recovery is to drill a vertical well at certain distance away from the
original well. Fluids such as gases or water are injected into one of the
wells under relatively high pressure. Oil and other fluids are produced
from the other well under relatively low pressure.
A drawback of using two vertical wells is poor volumetric sweep efficiency.
Injected fluids tend to take a short path between adjacent injection and
production wells that causes poor horizontal sweep. Gases tend to migrate
through the upper portion of the reservoir. Water tends to migrate through
the lower portion of the reservoir. These result in poor vertical sweep.
Poor horizontal sweep results from well configuration. Gas gravity
override and water gravity underride result from density differences
between injected and reservoir fluids. Another phenomenon leading to poor
volumetric sweep efficiency results from unfavorable mobility ratio.
Viscosity of injected fluids is lower than that of the reservoir oil,
which causes uneven frontal development known as viscous fingering. Even
if there were no density and viscosity differences, injected fluids could
still channel through more permeable strata, leaving a significant portion
of the formation volume upswept. An oil recovery method mitigating these
undesirable effects will enjoy increased oil recovery due to improved
volumetric sweep efficiency.
Two of the methods used to improve volumetric sweep efficiency pertinent to
this invention are gravity drainage and the use of horizontal wells. The
following reference to prior arts will be focused on gas injection because
gas injection is the preferred embodiment of this invention. After
injected gas breaks through a production well, oil production rate falls
off. Gas production rate increases. Excessive and early production of the
injected gases is undesirable. It reduces the overall recovery, prolongs
the operation, and imposes additional costs of processing and reinjecting
produced gases, as disclosed in U.S. Pat. No. 4,368,781, to Anderson.
The most effective method to minimize gas production is gravity drainage.
One of the earliest and probably the most widely used methods for gravity
drainage is to perforate a production well at the bottom portion of a
reservoir. Taking a horizontal cross section of the perforated zone, the
wellbore acts as a single point pressure sink. There is a large pressure
drop around the wellbore due to radial flow. The pressure drop is
proportional to production rate. For a low-permeability reservoir, oil
production rate is often limited by the parting pressure of the formation.
Numerous patent disclosures are related to horizontal wells. See Allen U.S.
Pat. No. 4,410,215, Brannan et. al. U.S. Pat. No. 5,273,111, Brown et. al.
U.S. Pat. No. 4,718,485, Huang et. al. U.S. Pat. Nos. 4,702,314, 5,065,821
and 5,320,170, Mullins et. al. U.S. Pat. No. 4,385,662, and Shu et. al.
U.S. Pat. No. 4,598,770. A horizontal production well acts as a linear
pressure sink. It provides a relatively large area for flow that results
in smaller pressure drop and improved volumetric sweep efficiency.
The above patents include methods of spatial arrangements of horizontal and
vertical wells. The purpose of this invention is not to disclose new well
arrangement patterns. Instead, it is to adapt high-permeability web to any
well arrangement configuration as known in the art. Therefore, only an
inverted 5-spot pattern and a pattern of parallel horizontal wells are
used as preferred embodiments. Inverted 5-spot patterns are found in many
oil fields. Such a pattern consists of one vertical injection well and
four vertical production wells. A modified inverted 5-spot pattern is
disclosed in U.S. Pat. No. 5,320,170 to Huang et. al., adding four
horizontal wells along the sides. The other preferred embodiment teaches
drilling laterally and vertically staggered horizontal wells as disclosed
in U.S. Pat. No. 5,237,111 to Brannan et. al.
Two of the technologies are modified and used to create a high-permeability
web around a vertical or horizontal well. One is high-pressure water jet
as disclosed in U.S. Pat. No. 5,413,184 to Landers. The other is
high-power microwave energy as disclosed in U.S. Pat. No. 5,299,887 to
Ensley. The high-pressure water jet cuts a channel into a formation at a
distance of 200 feet and beyond. The contemplated application of the
technique is to cut additional branches of channels at different locations
and directions. For the microwave technology, an antenna is lowered into a
production well to the bottom portion of an oil-bearing formation. The
antenna generates electromagnetic waves at selected frequencies. The
frequencies used for this application are in the Ghz range, or microwaves.
High-power microwave beams aimed horizontally will penetrate the formation
up to 100 feet. The microwave frequencies are selected to maximize
vaporization of hydrocarbons and water in the porous media. Because the
high-power microwave energy is delivered rapidly, vaporization is
completed in seconds or minutes. The sudden generation of large amounts of
gases will fracture the formation, resulting in a permeability increase of
several orders of magnitude, along the path of microwave penetration.
Produced gases return to the production well through the high-permeability
channel. The direction of microwave penetration is rotated until a desired
fracture pattern has been developed. The above technologies produce a
horizontal, high-permeability web around the wellbore. Because the entire
high-permeability web acts as the pressure sink, the pressure drop is
small.
Gravity drainage is also used in conjunction with any enhanced oil recovery
(EOR) method. The purpose of EOR is to improve mobility control and
displacement efficiency. Mobility control mitigates viscous fingering.
Improved displacement efficiency reduces residual oil saturation in the
pores that have been swept by the injected fluid. Common EOR methods
include thermal (e.g., steam and combustion), miscible (e.g., CO.sub.2),
and chemical (e.g. surfactant and polymer). Examples of recent disclosures
of EOR methods used with gravity drainage are thermally assisted gravity
segregation disclosed in U.S. Pat. No. 5,503,226 to Wadleigh; and
horizontal well gravity drainage combustion process disclosed in U.S. Pat.
No. 5,456,315 to Kisman, et. al.
Additional factors affecting gravity drainage are properties of the
reservoir and injected fluids, stratification and flow characteristics of
the porous media, oil field facilities, operation strategies, and process
economics. These factors will also affect the implementation of
high-permeability webs.
SUMMARY OF THE INVENTION
The present invention provides a novel and improved method for recovering
hydrocarbons from a subterranean formation. The method is applied to
primary and secondary recovery processes. It is also compatible with
horizontal and vertical well arrangement methods, enhanced oil recovery
methods, and methods used to improve the oil field conformance.
In a simple embodiment, the method is used to produce oil from primary
recovery mechanism, e.g., reservoir under strong gas cap or solution gas
drive. A vertical well is drilled into the oil-bearing formation. A
special horizontal well drilling tool then may be lowered into the well.
The tool generates one or more high-pressure water jet aimed at a
horizontal direction that cuts one or more horizontal channel through the
formation. At least four of these channels are drilled. Secondary channels
are also created by high-pressure water jet. The secondary channels branch
from the horizontal wells. A horizontal, high-permeability web has been
constructed at the bottom portion of the reservoir.
Another method of creating a high-permeability web is by high-power
microwave fracturing. In this method, an antenna is lowered from a mobile
microwave generation unit into the production well. One or more microwave
beams of controlled frequencies, direction, intensity, and duration are
applied to the adjacent formation. The microwave frequencies are chosen to
maximize vaporization of the reservoir fluids. The power used for this
application is in the megawatt range. The power intensity is maximized to
provide maximum penetration. Hydrocarbons and water in the porous media
are selectively vaporized by the microwave energy in seconds or minutes.
The sudden generation of large amounts of vapors induces fractures in the
path swept by the microwave, causing a permeability increase of many
orders of magnitude. Permeability of the fractured formation is typically
more than one Darcy. Generated vapors migrate toward the production well.
The location for microwave release can be placed within a channel created
by conventional or high-pressure water jet drilling.
The pressure in a high-permeability web is approximately equal to the
bottomhole pressure. This configuration facilitates gravity drainage. In
the oil-bearing zone, oil migrates downward. Gas migrates upward. The gas
breakthrough is delayed. The volumetric sweep is improved. The rate of oil
production is increased. The method also improves overall oil recovery.
In a further embodiment, the method of producing oil requires at least one
additional injection well. Fluids are injected into the upper portion of
the reservoir. The fluids include, but are not limited to, hydrocarbons,
CO.sub.2, steam, air, and flue gas. If there is a gas cap or a
high-permeability layer at the upper portion of the reservoir, gases are
injected into one of these structures. Otherwise, and if economically
warranted, a high-permeability web is created to facilitate injection
profile and injection rate. In this embodiment, injected fluids push oil
from the upper to the lower portion of the formation. Injected fluids are
also used to improve sweep and displacement efficiencies. Horizontal,
high-permeability webs are compatible with any enhanced oil recovery
method, as known in the art. In case of injecting a water based agent,
such as surfactant and polymer solution, the injection and production
configuration needs to be inverted. Water is injected into the bottom of
the reservoir. Oil is produced from the top of the reservoir.
For most of the oil field operations, it is necessary to implement more
than one injection well and one production well. The spatial arrangement
of wells requires technical and management decision. High-permeability
webs can be adapted to any well configurations as known in the art.
Examples are given to two preferred embodiments. One is an inverted 5-spot
pattern to take advantage of existing wells in a field. The other is
laterally and vertically staggered horizontal wells as disclosed in U.S.
Pat. No. 5,273,111 to Brannan et. al. An inverted 5-spot pattern has a
center injector and four corner producers. These wells are drilled
vertically. In a particular embodiment, four additional horizontal wells
are completed. The horizontal wells are connected to a corner producer.
Additional high-permeability branches are created to form a web. These
branches are connected to the horizontal well. If economically warranted,
a high-permeability web is also implemented to the center injector at the
upper portion of the reservoir. This configuration uses all of the
existing vertical wells in a 5-spot pattern. In the laterally and
vertically staggered horizontal wells, high-permeability webs are created
in the plane comprising the bottom horizontal production wells.
High-permeability webs are also created in the top horizontal injection
wells. Oil production schemes are the same as those described for one
injection well and one production well.
The method used for hydrocarbon recovery from subterranean formation also
depends on the properties of the formation and the reservoir fluids. Two
of the problems affecting a gravity drainage process are low-permeability
strata and bottom water coning. A low-permeability layer often acts as the
bottleneck for vertical flow. Sometimes, it is more economical to produce
from this formation as if there are two separate reservoirs. Sometimes, it
is necessary to heat or fracture the low-permeability layer. Some of the
heating and fracturing methods are disclosed in U.S. Pat. No. 5,449,889 to
Samardzija and U.S. Pat. No. 5,299,887 to Ensley. High-power microwave
technology is also used for the vitrification of rocks beneath the
water-oil contact to mitigate bottom water coning.
The methods disclosed in this invention are also applicable to gas and gas
condensate reservoirs and are modified for applications to heavy oil,
shale oil and tar sands.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic illustration of a hydrocarbon reservoir in a
subterranean formation in the process of being modified for enhanced
production according to an embodiment of the present invention.
FIG. 2 is a top cross-sectional view of the high-permeability web formed
according to the method of FIG. 1.
FIG. 3 is a diagrammatic illustration of a hydrocarbon reservoir in a
subterranean formation in the process of being modified for enhanced
production according to an alternative embodiment of the present
invention.
FIG. 4 is a top cross-sectional view of the high-permeability web formed
according to the method of FIG. 3.
FIG. 5 is a diagrammatic illustration of a hydrocarbon reservoir in a
subterranean formation in the process of being modified for enhanced
production according to an alternative embodiment of the present
invention.
FIG. 6 is a diagrammatic illustration of a hydrocarbon reservoir in a
subterranean formation in the process of being modified for enhanced
production according to an alternative embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The methods of the present invention provide improved means for recovering
hydrocarbons from a subterranean formation. The methods of creating
high-permeability webs are applied to primary and secondary oil recovery
processes. They are also used in conjunction with horizontal and vertical
well arrangement methods, enhanced oil recovery methods, and methods used
for conformance enhancement.
In a simple embodiment, the method is used to produce oil from primary
recovery mechanism, e.g., a reservoir under strong gas cap or solution gas
drive, as shown in FIG. 1. The reservoir is confined at the top and the
sides in a dome formation 1. It contains a gas cap 2 and is bounded by an
aquifer 3 at the bottom. A vertical well 4 is drilled into the oil-bearing
formation 5. A method is used to create a high-permeability web 6 at the
bottom portion of the reservoir. In this embodiment, a high-power
microwave antenna 7 such as disclosed in U.S. Pat. No. 5,299,887 to Ensley
is lowered into the well. The antenna generates a microwave beam 8, of
controlled frequencies, direction, intensity, and duration. The
frequencies are selected to maximize vaporization and pyrolysis of
hydrocarbons and water in the reservoir. For this application, it is
desirable to keep the microwave intensity high in order to achieve maximum
penetration. High intensity results from high power and low area of
exposure. Exposed hydrocarbons and water in the porous media are
selectively vaporized, usually in seconds or minutes. The sudden
generation of large amounts of vapors induces fractures in the path swept
by microwave, causing a permeability increase of many orders of magnitude.
Permeability of the fractured formation is typically more than one Darcy.
Generated vapors migrate toward the production well. The direction of the
microwave beam is substantially horizontal. A single beam or an array of
beams aimed at different directions are generated simultaneously. Multiple
applications are made to create a horizontal radial high-permeability web
6 shown in FIG. 2. This figure is a horizontal plane containing the web.
The center of the web is the vertical production well 4 containing
microwave antennae. The fractured zones 9 are the high-permeability webs
created by microwave. The well is then put on production. Pressure in the
high-permeability web is approximately equal to the bottomhole pressure.
This pressure profile facilitates gravity drainage. In the oil-bearing
zone, oil migrates downward. Gas migrates upward. The gas breakthrough is
delayed. The volumetric sweep is improved. The rate of oil production is
increased. It is contemplated that the overall oil recovery will also
increase.
In an elaborate embodiment, the method of producing oil requires at least
one additional injection well 10. The method is depicted in FIG. 3. In
this embodiment, a different method of implementing a high-permeability
web is illustrated. Four horizontal wells 11, 90 degrees apart, are
drilled using conventional or high-pressure water jet drilling technology,
as disclosed in U.S. Pat. No. 5,413,184 to Landers or as is known in the
art. An antenna 7 or a flexible hose 12 is then inserted into one of these
horizontal wells. The antenna generates high-power microwave. The flexible
hose generates high-pressure water jet streams. In a preferred embodiment,
multiple microwave or water jet beams are radiated from at least one point
in a horizontal well, which creates a high-permeability web 6 as shown in
FIG. 4. This figure includes the horizontal plane containing the web. The
center of the web is the vertical production well 4. The four stems away
from the center are the horizontal wells 11. The microwave antenna 7 or
the spray head 13 is placed in a position to generate high-permeability
webs. Multiple streams of microwave beams or water jets are shot into the
formation, creating an array of high-permeability channels. If there is a
gas cap or a high-permeability layer 14 at the upper portion of the
reservoir, gases can be injected into one of these structures. Otherwise,
and if economically warranted, a high-permeability web is created to
facilitate injection profile and injection rate. Oil in strata above the
layer used for injection is recovered as known in the art as attic oil. In
this embodiment, fluids are injected into the upper portion of the
reservoir. Injected fluids push oil downward. They are used to enhance
volumetric sweep efficiency and improve overall oil recovery. The fluids
include, but are not limited to, hydrocarbons, CO.sub.2, steam, air, and
flue gas. Any enhanced oil recovery method as known in the art is
compatible with the high-permeability web. In case a water based agent,
such as surfactant and polymer solution, is injected, the injection and
production configuration is inverted. Water is injected into the bottom of
the reservoir. Oil is produced from the top of the reservoir.
For most of the oil field operations, it is necessary to implement more
than one injection well and one production well. The spatial arrangement
of wells requires a technical and management decision. High-permeability
webs are adapted to a particular well configuration as known in the art.
Examples are given to two preferred embodiments. One is an inverted 5-spot
pattern to take advantage of existing wells in the field. The other is a
laterally and vertically staggered horizontal wells as disclosed in U.S.
Pat. No. 5,273,111 to Brannan et. al. An inverted 5-spot pattern has a
center injector 10 and four corner producers 4, as shown in FIG. 5. These
wells are drilled vertically. A high-permeability web 6 is implemented to
each of the producers at the bottom portion of the reservoir. If
economically warranted, a high-permeability web is also implemented to the
center injector. In this particular embodiment, four horizontal wells 11
are completed. The horizontal wells are connected to the corner producers.
Additional high-permeability branches are also created to form a
high-permeability web. These branches are connected to the horizontal
wells.
The second preferred embodiment is to apply high-permeability webs to
laterally and vertically staggered horizontal wells as shown in FIG. 6.
This application is most suitable for newly developed oil fields. The
distance between wells depends on the depth of penetration by microwave
and/or high-pressure water jet. As a rule of thumb, the further the
penetration, the further the distance between adjacent wells.
High-permeability webs are created in the plane comprising the bottom
horizontal production wells 15. High-permeability webs are also created
for the top horizontal injection wells 16. The webs are connected to the
horizontal wells. Oil recovery schemes are the same as those described for
one injection well and one production well.
The method used for hydrocarbon recovery from subterranean formation also
depends on the properties of the formation and the reservoir fluids. Two
of the problems affecting a gravity drainage process are low-permeability
strata and bottom water coning. A low-permeability layer often acts as the
bottleneck for vertical flow. Sometimes, it is more economical to produce
from this formation as if there are two separate reservoirs. Sometimes, it
is necessary to heat or fracture the low-permeability layer. The methods
used for heating and fracturing are disclosed in U.S. Pat. No. 5,449,889
to Samardzija and U.S. Pat. No. 5,299,887 to Ensley. High-power microwave
technology is also used for the vitrification of rocks beneath the
water-oil contact to mitigate bottom water coning.
The methods disclosed in this invention are also applicable to gas and gas
condensate reservoirs and are modified for applications to heavy oil,
shale oil and tar sands.
One of the problems at a production well is water conning. To mitigate this
problem, microwave technology is used to perform an in-situ vitrification.
This can be accomplished by sending a microwave beam at a selected
wavelength that will melt the matrix rock below the water-oil contact.
This invention discloses methods of oil recovery based on conformance
enhancement, particularly, the generation and use of high-permeability
webs. It is contemplated that these methods will improve overall
hydrocarbon recovery from subterranean formations and the process
economics.
All patents and publications mentioned in this specification are indicative
of the levels of those skilled in the art to which the invention pertains.
All patents and publications are herein incorporated by reference to the
same extent as if each individual publication was specifically and
individually indicated to be incorporated by reference.
The present invention, therefore, is well adapted to carry out the objects
and attain the ends and advantages mentioned as well as others inherent
therein. While presently preferred embodiments of the invention are given
for the purpose of disclosure, numerous changes in the details will
readily suggest themselves to those skilled in the art and which are
encompassed within the spirit of the invention and the scope of the
appended claims.
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